Microanalysis device

ABSTRACT

Microstructure for fluids provided in a rotatable disc (D) having a U-shaped volume-defining structure ( 7 ) connected at its base to an inlet arm of a U-shaped chamber ( 10 ).

FIELD OF THE INVENTION

[0001] The present invention relates to microanalysis devices andmethods for moving fluids in such devices.

PRIOR ART

[0002] The idea is applicable to (but not limited to) micro-analysissystems that are based on microchannels formed in a rotatable, usuallyplastic, disc, often called a “centrifugal rotor” or “lab on a chip”.Such discs can be used to perform analysis and separation on smallquantities of fluids. In order to reduce costs it is desirable that thediscs should be not restricted to use with just one type of reagent orfluid but should be able to work with a variety of fluids. Furthermoreit is often desirable during the preparation of samples that the discpermits the user to dispense accurate volumes of any desired combinationof fluids or samples without modifying the disc. Due to the small widthsof the microchannels, any air bubbles present between two samples offluids in the microchannels can act as separation barriers or can blockthe microchannel and thereby can prevent a fluid from entering amicrochannel that it is supposed to enter. In order to overcome thisproblem U.S. Pat. No. 5,591,643 teaches the use of a centrifugal rotorwhich has microchannels that have cross sectional areas which aresufficiently large that unwanted air can be vented out of themicrochannel at the same time as the fluid enters the microchannel.

OBJECT OF THE INVENTION

[0003] An object of the present invention is to provide a structure fora centrifugal rotor and a method for using such a centrifugal rotor,which structure and which method permits the reliable transport offluids in the centrifugal rotor.

[0004] A further object of the present invention is to provide astructure for a centrifugal rotor and a method for using such acentrifugal rotor, which structure and which method permits the accuratemetering of fluids in the centrifugal rotor.

SUMMARY OF THE INVENTION

[0005] The present invention achieves the objects of the invention bymeans of a structure having the features of claim 1. A method for usingsuch a structure to achieve the objects of the invention has thefeatures of claim 5.

BRIEF DESCRIPTION OF THE FIGURES

[0006] The present invention will be illustrated by a non-limitingexample of an embodiment by means of the following figures, where:

[0007]FIG. 1a shows the peripheral part of a centrifugal rotor havingfive radially extending microchannel structures K7-K12 in accordancewith the present invention;

[0008]FIG. 1b shows an enlarged view of one microchannel structure fromFIG. 1a in accordance with the present invention;

[0009]FIG. 1c shows an enlarged view of a sample volume-definingstructure in the microchannel structure of FIG. 1b;

[0010]FIG. 1d shows an enlarged view of the chamber area plus chambersfor the disposal of waste fluids, wherein variations in depth are shownby cross-hatching;

[0011]FIGS. 2a and 2 b show the structure of FIG. 1b with the chambercontaining a first fluid;

[0012]FIGS. 3a and 3 b shows the addition of a second fluid to avolume-defining chamber;

[0013]FIGS. 4a and 4 b show the replacement of the first fluid in thechamber by said second fluid;

[0014]FIG. 5 shows a second embodiment of a microchannel structure inaccordance with the present invention;

[0015]FIG. 6 shows a third embodiment of a microchannel structure inaccordance with the present invention; and

[0016]FIG. 7 shows a fourth embodiment of a microchannel structure inaccordance with the present invention.

[0017]FIG. 8 shows a fifth embodiment of a microchannel structure inaccordance with the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS ILLUSTRATING THE INVENTION

[0018] The microchannel structures (K7-K12) in accordance with thepresent invention are shown in FIGS. 1a-d arranged radially on amicrofluidic disc (D). Suitably the microfluidic disc is of a one- ortwo-piece moulded construction and is formed of an optionallytransparent plastic or polymeric material by means of separate mouldingswhich are assembled together (e.g. by heating) to provide a closedstructure with openings at defined positions to allow loading of thedevice with fluids and removal of fluid samples. Suitable plastic ofpolymeric materials may be selected to have hydrophobic properties.Preferred plastics or polymeric materials are selected from polystyreneand polycarbonate. In the alternative, the surface of the microchannelsmay be additionally selectively modified by chemical or physical meansto alter the surface properties so as to produce localised regions ofhydrophobicity or hydrophilicity within the microchannels to confer adesired property. Preferred plastics are selected from polymers with acharged surface, suitably chemically or ion-plasma treated polystyrene,polycarbonate or other rigid transparent polymers.

[0019] The microchannels may be formed by micro-machining methods inwhich the micro-channels are micro-machined into the surface of thedisc, and a cover plate, for example, a plastic film is adhered to thesurface so as to enclose the channels. The microfluidic disc (D) has athickness which is much less than its diameter and is intended to berotated around a central hole so that centrifugal force causes fluidarranged in the microchannels in the disc to flow towards the outerperiphery of the disc. In the embodiment of the present invention shownin FIG. 1a-1 d, the microchannels start from a common, annular innerapplication channel (1) and end in common, annular outer waste channel(2), substantially concentric with channel (1). It is also possible tohave individual application channels (waste channels for eachmicrochannel or a group of microchannels. Each inlet opening (3) of themicrochannel structures (K7-K12) may be used as an application area forreagents and samples. Each microchannel structure (K7-K12) is providedwith a waste chamber (4) that opens into the outer waste channel (2).Each microchannel (K7-K12) forms a U-shaped volume-defining structure(7) and a U-shaped chamber (10) between its inlet opening (3) and thewaste chamber (4). The normal desired flow direction is from the inletopening (3) to the waste chamber (4) via the U-shaped volume-definingstructure (7) and the U-shaped chamber (10). Flow can be driven bycapillary action, pressure and centrifugal force, i.e. by spinning thedisc. As explained later, hydrophobic breaks can also be used to controlthe flow. Radially extending waste channels (5), which directly connectthe annular inner channel (1) with the annular outer waste channel (2),in order to remove an excess fluid added to the inner channel (1), arealso shown.

[0020] Thus, fluid can flow from the inlet opening (3) via an entranceport (6) into a volume-defining structure (7) and from there into afirst arm of a U-shaped chamber (10). The volume-defining structure (7)is connected to a waste outlet for removing excess fluid, for example,radially extending waste channel (8) which waste channel (8) ispreferably connected to the annular outer waste channel (2). The wastechannel (8) preferably has a vent (9) that opens into open air via thetop surface of the disk. Vent (9) is situated at the part of the wastechannel (8) that is closest to the centre of the disc and prevents fluidin the waste channel (8) from being sucked back into the volume-definingstructure (7).

[0021] The chamber (10) has a first, inlet arm (10 a) connected at itslower end to a base (10 c) which is also connected to the lower end of asecond, outlet arm (10 b). The chamber (10) may have sections I, II,III, IV which have different depths, for example each section could beshallower than the preceding section in the direction towards the outletend, or alternatively sections I and III could be shallower thansections II and IV, or vice versa. A restricted waste outlet (11), i.e.a narrow waste channel, is provided between the chamber (10) and thewaste chamber (4). This makes the resistance to fluid flow through thechamber (10) greater than the resistance to fluid flow through the paththat goes through volume-defining structure (7) and waste channel (8).

[0022] Due to the relatively large width of the waste chamber (4), thetop and bottom surfaces of the waste chamber (4) are preferablyseparated by one or more supports (12) to ensure that the top and bottomsurfaces of the microfluidic device do not bend inwards towards thewaste chamber (4) and thereby change its volume.

[0023] As shown in FIGS. 1a-c, the volume-defining structure (7) isU-shaped with the entrance port (6) opening into the upper end (i.e. theend nearest to the centre of the disc) of one of the arms (7 a) of the Uand the waste channel (8) connected to the upper end of the other arm (7b) of the U. The vent (9) is also placed at the top of this other arm (7b). The base (7 c) of the U-formed volume-defining structure (7) isconnected to the upper end of a first arm (10 a) of the chamber (10).

[0024] In addition to the application area at the inlet (3) of thestructure, there may also be an additional application area (13) thatopens out into the top surface of the disc and is connected to theentrance port (6). This additional application area (13) can be usedwhen it is desired to add different reagents or samples to each of thedifferent microstructures (K7-K12).

[0025] There is preferably also a vent (14) to open air in the chamber(10). A hydrophobic break is preferably provided at the connection (16)of the chamber (10) to the volume-defining structure (7) in order toguide fluid into arm (7 b)

[0026] The outer annular waste channel (2) may be sectioned so as tocollect waste from a selected number of closely located microchannelstructures.

[0027] Hydrophobic breaks can be introduced into the microchannelstructures (K7-K12), for example by marking with an over-head pen(permanent ink) (Snowman pen, Japan), and suitable places for suchbreaks (shown by crosshatching in the figures) include: (a) betweenmicrochannel structure inlets (3) in the inner annular applicationchannel (1), (b) each opening (15) into the outer annular waste channel(i.e. the openings of the waste chambers) and, (c) if present, also theradial waste channels (5) which connect the inner annular applicationchannel (1) and the outer annular waste channel (2), and also the wastechannel (8) which guides away excess fluid from the volume-definingstructure (7).

[0028] The purpose of the hydrophobic breaks is to prevent capillaryaction from drawing the fluid into undesired directions. Hydrophobicbreaks can be overcome by centrifugal force i.e. by spinning the disc athigh speed.

[0029] If the sample to be analysed is in the form or cells orsedimenting material or particles then it can be held in the lowerU-channel by a particle filter (21) (shown by a dotted line in FIG. 1band 1 d) or the flow through the chamber (10) can be controlled suchthat particles are retained in the chamber while fluids flow throughit—as will be described later.

[0030] A first reagent or sample fluid X can be introduced into thechamber (10) by connecting a source (not shown) of the fluid X to thecommon annular inner application channel (1) from where it flows bycapillary action and/or, if the disc is spun, centrifugal force to thelower U-bend. If the volume of fluid X which is introduced into commonannular inner application channel (1) is in excess (i.e. is greater thanthe volume of the chamber (10) up to the level of the restricted channel(11) (distance L4 in FIG. 1d)) then some of it flows to waste via theradial waste channel (5) while the rest flows to waste chamber (4) viathe chamber (10) though the restricted channel (11) as shown in FIG. 2.This continues until the levels of fluid X in both the left hand andright hand arms of the chamber (10) are the same as the distance L4,i.e. the U-shaped chamber is full up to the level of the restrictedchannel (11). This is shown in FIG. 2b) where the excess fluid X hasflowed out of the microchannel structure via the waste chamber (4) andradial waste channel (5) to the outer waste channel (2) or via therestricted channel (11).

[0031] When it is time to add a new reagent or sample fluid Y, thenfluid Y is added by the common annular inner application channel (1)(or, alternatively, as shown in FIG. 3a) by the additional applicationarea (13)). The fluid Y travels by capillary action through thevolume-defining structure (7) and down the waste channel (5) as shown inFIG. 3a). It cannot flow into chamber (10) as the air cushion (19)contained between the base of the volume defining structure and the topof the fluid in arm (7 a) of the chamber acts as a barrier to preventthe fluid flowing into chamber 10. Note that optionally an air cushion(19) can be left between the first fluid X and the second fluid Y bymaking the distance L4 from the base of the U-bend in the chamber (10)to the restricted channel (11) less than the distance L3 from the baseof the U-bend in the chamber (10) to the base of the U-bend of thevolume-defining structure (7).

[0032] This can prevent the second fluid Y from flowing by capillaryaction into the chamber (10) and can also prevent mixing of the fluids Xand Y. The vent (9), which is open to atmospheric pressure, makes iteasier for the second fluid Y to flow towards the waste channel (5).Gentle, i.e. low speed, spinning of the disc (D) empties the excessfluid Y from waste channel (5), leaving the volume-defining structure(7) full of fluid Y, as shown in FIG. 3b).

[0033] All of the first fluid X in the chamber (10) can be displaced bythe second fluid Y by spinning the disc if the volume of the secondfluid in the volume-defining structure (7) and any air between the firstand second fluids is equal to or greater than the volume of the firstfluid X in the chamber (10). This can be achieved by ensuring that thevolume of the volume-defining structure (7) is greater than the volumeof the chamber (10). This can be achieved by making the arms (7 a) and(7 b) of the volume-defining structure longer than the arms of thechamber (10), and/or by making the cross-sectional area of the arms ofthe volume-defining structure (7) greater than that of the arms of thechamber (10). FIG. 4a) shows an intermediate situation where the disc isbeing spun and centrifugal force causes fluid Y to flow from thevolume-defining structure (7) into chamber (10), thereby displacingfirst fluid X which flows to waste via restricted channel (11). Anyexcess second fluid Y flows out of the chamber (10) through therestricted channel (11) into waste chamber (4). FIG. 4b) shows that thesecond fluid Y has replaced the first fluid X. This process can berepeated using different fluids as often as is desired.

[0034] In the event that the fluids contain particles and it is desiredto hold them in the chamber it is possible to provide the chamber (10)with a particle filter (21) with suitable sized orifices. In the eventthat it is necessary to only temporarily hold the particles in thechamber (10) then the sections I, II, III, IV of the chamber (10) whichhave different depths can be used to temporarily trap the particles.This is done by increasing the speed of rotation of the disc so that theparticles collect at the boundary wall between two sections while thefluid flows over the wall.

[0035] In another aspect of the invention, particles can be selectivelyheld in, or flushed out of a chamber (10′), which does not have aparticle trap or sections having different depths as shown in FIG. 5.This can be achieved as follows:

[0036] Particles that have been sedimented, or otherwise collected, inthe bottom of the chamber (10′) can be drawn out of the chamber (10′) bythe meniscus of a fluid which flows out of the chamber (10′). In otherwords, if there is an air cushion (19′) between the volume-definingstructure and the chamber (10′) and this is driven through the chamber,then as the meniscus between the fluid in the chamber and the aircushion passes the particles they are entrained by the meniscus and flowout of the chamber. This can be achieved by choosing a suitably low rateof acceleration of the disc (known as “ramp speed”). If however it isdesired to retain the particles in the chamber then it is necessary toensure that the air cushion is not driven through the chamber (10′) bythe fluid in the volume-defining structure when the disc is spun. If asuitably high rate of acceleration of the disc is chosen, it is possibleto cause the fluid in the volume-defining structure to flow down thesides of the channel, through the air cushion (19′), without displacingthe air cushion (19′). Typically a ramp speed of up to 3500 rpm/s²transports the particles further in the channel system. With a rampspeed greater than 3500 rpm/s² the fluid/air interface (meniscus) doesnot enter the U-chamber and the air bubble stays still or moves in theopposite direction to the centrifugal force. The exact ramping speeds toachieve the desired effect are naturally dependent on the type of fluidused and are most suitably determined by experimentation.

[0037] In another embodiment of the invention, as shown in FIG. 6, thearm (7 b′) of the volume-defining structure (7′) is not connected to awaste channel (8), but is instead enlarged at its end nearest the centreof the disk in order to form a reservoir (61) for fluid to prevent fluidoverflowing out of a vent (9′). This vent and/or sample inlet (9′) ventsthis reservoir (61) to atmosphere and can also permit samples to beintroduced into the structure. The reservoir (61) preferably has alength which makes the length of the volume defining structure i.e.reservoir (61) and arm (7 b′) equal to or greater than the length of arm(7 a′). If the vent (9′) is made so small that the surface tension ofthe fluid prevents it from flowing out of the vent when thevolume-defining structure (7′) is being charged by spinning, then theamount of fluid which can enter the volume-defining structure (7′) isminimised and no fluid is wasted. Naturally if it is desired to replaceall the fluid in the chamber (10) with fluid from the volume definingstructure then the volume of the volume defining structure must begreater than the volume of the chamber (10). If the arm (10 a) of thechamber is made to widen from its upper end to its lower end then it ispossible to push the air barrier (19) out of the chamber when adding asecond fluid without the two fluids mixing.

[0038] All the chambers of the present invention can be provided withheating means in the form of a coating as shown crosshatched in FIG. 7.This coating (71), which can be painted or printed or applied in someother way to one or both sides of the disk in the vicinity of thechamber, can absorb energy from electromagnetic radiation which isdirected onto it and thereby heat up the chamber. The incident radiationcan be infra red light, laser light, visible light, ultraviolet light,microwaves or any other suitable type of radiation. The heating up ofthe chamber can be used to initiate or accelerate reactions in thechamber. If the disk is stationary while the chamber is being heatedthen if the fluid boils it will produce bubbles of vapour which willtravel up the arms of the chamber and may even pass out into the wastechannel (8) and waste chamber (4). This is not always desirable as it isoften preferred that substantially all the fluid should remain in thechamber after the heating has been finished. This can be achieved in thepresent invention by spinning the disk at the same time that radiationis incident on the coating (71). The radiation sources (not shown) canbe focused onto areas that the coating passes through as the disc spins.Furthermore the coating can be dimensioned such that heat is onlyapplied to only the smallest amount of the base consistent with adequateheating of the reagents. In this way the arms of the U are keep cool andprovide condensation surfaces for the fluid vapour to condense on. Thecentrifugal force exerted on the condensed vapour causes it to flow backinto the base of the chamber.

[0039] Note that while the embodiments of the invention described abovehave a chamber leading to a waste chamber, it is of course conceivablethat the chamber outlet leads to one or more further chamber(s). Eachfurther chamber may have a plurality of inlets and a plurality ofoutlets so that samples and reagents may be combined in a chamber. Thesubsequent results of any process, which has taken place in a chamber,can be dispensed to one or more additional chambers for furtherprocessing or sent to the waste channel. An example of this is shown inFIG. 8. FIG. 8 shows a microstructure, of a design similar to that shownin FIG. 6, in which the base (110 c) of U-shaped chamber (110) isconnected by a base outlet channel (134) to a second chamber (136),which second chamber (136) is positioned further away from the centre ofthe disk than second chamber (110). Second chamber (136) is vented toatmosphere by a vent (138) that opens out on the top surface of thedisc. Second chamber (136) is also provided with an inlet/outletconnection (140) that also opens out on the top surface of the disk.Inlet/outlet (140) can be used to supply substances to second chamber(136) e.g. by injecting them into connection (140) and/or to extractsubstances from second chamber (136) e.g. by sucking them out viaconnection (140). Fluid is prevented from flowing by capillary actionfrom chamber (110) into base outlet channel (134) by a hydrophobic break(132) positioned at or near the junction (130) between the base (110 c)of chamber (110) and base outlet channel (134). Hydrophobic break (132)is dimensioned so that when the disc is spun at a certain number ofrevolutions per second then any fluid in chamber (110) leaves thechamber via chamber outlet arm (110 b), and when the disc is spun at ahigher number of revolutions per minutes then the centrifugal forceacting on the fluid is sufficient to overcome the hydrophobic effect ofhydrophobic break (132) and the fluid flows into second chamber (136).In this embodiment of the present invention, the outlet arm (110 b) ofchamber (110) is almost as long as inlet arm (110 a). Thus when chamber(110) is filled with a fluid the level of fluid in inlet arm (110 b)will be very close to the base (107 c′) of the volume-defining structure(107′). This means that when a second fluid is supplied to thevolume-defining structure (107′), e.g. via inlet (109′) in the reservoir(161), it will come into direct contact with the first fluid in thechamber (110) and no air bubble will form between the two fluids. Thisarrangement can be used to facilitate mixing of two fluids.

[0040] The above mentioned examples of conceivable embodiments areintended to illustrate the present invention and are not intended tolimit the scope of protection claimed by the following claims.

1. Microstructure for fluids provided in a rotatable disc (D)characterised in that it comprises a U-shaped volume-defining structure(7, 107) comprising: a first arm (7 a) connected at or near its upperend to an entrance port (6) wherein the lower end of said first arm (7a) is further from, or the same distance from, the centre of said disc(D) than/as, said entrance port (6); a second arm (7 b) connected at ornear its upper end to a first waste channel (8) wherein said wastechannel (8) is further away from the centre of said disc (D) than saidentrance port (6); and a base (7 c) positioned further from said centreof said disc (D) than said first and second arms (7 a, 7 b) and whichbase (7 c) connects the lower ends of said first and second arms (7 a, 7b), wherein said base (7 c) is connected to an inlet arm (10 a, 110 a)of a U-shaped chamber (10, 110), at or near to the upper end of saidinlet arm (10 a), wherein said U-shaped chamber (10, 110) furthercomprises; a base (10 c, 110 c) and an outlet arm (10 b, 110 b), whereinsaid base (10 c, 110 c) connects the lower end of said inlet arm (10 a,110 a) to the lower end of said outlet arm (10 b, 110 b), and saidoutlet arm (10 b, 110 b) is connected at or near its upper end to asecond waste outlet (11) and said base (10 c, 110 c) is further from, orthe same distance from, the centre of said disc (D) than/as the lowerends of said inlet and outlet arms (10 a, 10 b; 110 a, 110 b) of saidU-shaped chamber (10, 110).
 2. Microstructure in accordance with claim 1characterised in that said first waste channel (8) is provided with avent (9).
 3. Microstructure in accordance with any of claims 1 or 2characterised in that the resistance to fluid flow through said secondwaste outlet (11) is greater than the resistance to fluid flow throughsaid first waste channel (8).
 4. Microstructure in accordance with anyof the previous claims characterised in that the length of the firstU-shaped volume-defining structure (7, 107) is greater than the lengthof the second U-shaped chamber structure (10, 110).
 5. Microstructure inaccordance with any of the previous claims characterised in that saidchamber structure (10, 110) is at least partly covered by a coating(71), which can absorb energy from electromagnetic radiation which isdirected onto it and thereby heat up said chamber structure (10). 6.Microstructure in accordance with any of the previous claimscharacterised in that in said chamber structure (10, 110) has sectionsI, II, III, IV which have different depths and which can be used to trapand release sedimenting material or other particles.
 7. Microstructurein accordance with any of the previous claims characterised in that insaid chamber structure (110) is connected by its base (110 c) to asecond chamber (136) positioned further from said centre of said disc(D) than said chamber structure (110) by means of a channel (134),wherein there is a hydrophobic break (132) positioned at or near thejunction (130) between the chamber (110) and the channel (132).
 8. Theuse of a microstructure in a rotatable disc (D) in accordance with anyof the previous claims to dispense predetermined volumes of fluid to achamber (10, 110) in said rotatable disk.
 9. Method for replacing afluid in a chamber (10, 110) in a rotatable disk (D) characterised bythe steps of: providing a microstructure in accordance with any ofclaims 1-7; filling said volume-defining structure (7) with areplacement fluid; and rotating said disk (D) at a sufficiently highspeed such that said replacement fluid moves under centrifugal forceinto said chamber while at the same time the original fluid in thechamber (10) is forced out of the chamber by the incoming replacementfluid.